1. Technical Field
The present invention relates to a thin film forming method using a droplet discharge method and a color filter manufacturing method using the thin film forming method.
2. Related Art
Attention has been paid to thin film forming techniques using a droplet discharge method in recent years. A key feature of the droplet discharge method is that the method allows applying a minute liquid to desired positions in accordance with the resolution of a droplet discharge head so that a minute pattern or thin films having a desired thickness is easily formed. The droplet discharge method having such a feature has been used in a color filter manufacturing process in which colors must be selectively applied in a minute manner, for example, by discharging a liquid, in which a material for forming colored layers (thin films) is dissolved or dispersed in a solvent.
One of the characteristics of a droplet discharge head with respect to the discharge of a liquid is unevenness, albeit slight, in amount of the discharged liquid (hereafter may be referred to as a “discharge amount”) among nozzles due to such as an error caused when forming thin films. This unevenness in discharge amount causes differences in thickness among formed thin films (unevenness in film thickness). For this reason, various methods for preventing such unevenness by controlling the amounts of the liquid discharged from individual nozzles have been proposed. For example, JP-A-2003-159787 proposes a droplet discharge head that is allowed to restrict the discharge of a droplet from a nozzle whose droplet discharge amount is significantly different from a predetermined value so as to reduce differences in discharge amount as a whole.
Incidentally, unevenness in thickness of formed thin films is also caused by a factor other than unevenness in discharge amount among the discharge nozzles.
For example, if thin films are formed using the droplet discharge method, minute droplets of a liquid are discharged and applied to a substrate with a high resolution; however, the liquid discharged on the substrate on which thin films are to be formed is dried extremely rapidly. Also, partial pressure applied to solvent molecules to be evaporated from the liquid composition in a peripheral area of an application area on the substrate is lower than that in the central area thereof. In other words, the solvent vapor concentration in the peripheral area is lower than that in the central area. Accordingly, the solvent evaporates more rapidly in the peripheral area than in the central area. With the evaporation of the solvent, for example, a flow of the liquid from the inside thereof toward a surface thereof occurs inside the disposed liquid. In this case, the state of the flow in an area where the solvent evaporates actively is different from that in an area where the solvent does not evaporate actively. As a result, there occurs a difference in state of formed films between these areas.
FIGS. 10A and 10B are schematic drawings showing states where thin films are formed by disposing a liquid L including a thin film forming material in a reception part 200 under environments that are different from each other in state of the evaporation of a solvent. Specifically, FIG. 10A shows a state in which a film is formed under an environment where a solvent does not evaporate actively and corresponds to the state of film forming in the above-mentioned central area of the application area. FIG. 10B shows a state in which a film is formed under an environment where a solvent evaporates actively and corresponds to the state of film forming in the above-mentioned peripheral area of the application area.
As shown in FIG. 10A, a flow of the liquid does not occur actively inside the disposed liquid under an environment where a solvent does not evaporate actively. Therefore, the shape of a formed thin film F reflects the shape of the disposed liquid droplet, that is, a central area FC of the thin film F rises in a convex manner.
On the other hand, as shown in FIG. 10B, a flow of the liquid such as one from the inside thereof toward a surface thereof occurs actively inside the disposed liquid under an environment where a solvent evaporates actively. For the same reason, even inside the disposed liquid, the solvent evaporates more actively in the peripheral area of the liquid L than in the central area thereof. Therefore, a flow from the central area toward the peripheral area occurs actively inside the liquid L so that the material for forming the thin film F accumulates more in the peripheral area. As a result, the thin film F is formed in such as manner that the peripheral area thereof is thick and the central area thereof is concave.
As is understood from the above description, there occurs a difference in state between areas of a formed film in accordance with the state of evaporation of the solvent. The difference in state between areas of a film manifests itself in the form of a difference in film thickness (unevenness in film thickness) attributable to a bump and a dip in the central area of the thin film. This results in a display failure (unevenness in display).